Following axotomy, olfactory receptor cell neurons degenerate and then regenerate forming new axonal connections with the central nervous system tissue dorsal to the cribriform plate. If portions of the olfactory bulb are left intact, connections are established but the anatomical arrangement of glomeruli and mitral cells is highly abnormal. If not all axons are disconnected during surgery, the part of the bulb which the preserved axons innervate retains some normal morphology. Our preliminary studies have shown that regenerated olfactory axons of rats bulbectomized when neonates form new and aberrant connects in the forebrain but are unable to detect odors. However, if a remnant of disconnected bulb is left in place, it is reinnervated by olfactory cell axons and such animals are capable of detecting and discriminating odors. The purpose of the proposed research is to replicate and expand these findings. Behaviorally, the classes of odors tested will be expanded, and both the degree of sensitivity and the ability to discriminate among odors will be studied. These behavioral data will then be correlated with the anatomical organization of the olfactory bulb remnant, its innervation pattern, immunohistochemical and electron microscopic assessment of the olfactory reconnection, and with the afferent and efferent connections of the bulb remnants as compared with the normal situation. The experiments are designed to gain further information relating to the plasticity of the system and to the underlying mechanisms involved in olfactory processes of odor detection and recognition, particularly with regard to the proposed idea of topography in the system.